The Two Ways to Progress VO2max Intervals (And Why You Only Pick One at a Time)

Progressive overload is non-negotiable in strength training. Most CrossFit or strength coaches know to either increase reps or intensity over time. Fewer apply that logic to aerobic work. With VO2max intervals there are exactly two progression levers, and moving both at once is how blocks fall apart by week three.

The Two Levers

Lever 1: Interval duration. Keep the intensity fixed, add time per interval each week. A starting block of 4×4 min at 110% FTP progresses to 4×5, then 4×6 at the same percentage. More total work, same relative intensity.

Lever 2: Intensity percentage. Keep the duration fixed, raise the percentage each week. 4×4 min at 110% FTP becomes 112%, then 114%. Same duration, harder effort.

Both drive adaptation. More duration means more total time at high oxygen uptake. Higher intensity pushes closer to true VO2max. Either one, applied consistently over 3–4 weeks, works. Both at once doesn't.

Why You Only Pick One

When you increase duration and intensity at the same time and a session falls apart, you don't know which variable broke it. You can't diagnose, so you can't fix it. You're just guessing.

There's also a timing problem. VO2max development is slow — a minimum of four weeks before measurable change shows up, often longer in well-trained athletes. The training needs to hold up across that whole window. One lever gives you that. Two levers tends not to.

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What a Simple Block Looks Like

Starting point for a strength-background athlete:

• Week 1: 4×4 min at 110% FTP, 4 min rest

• Week 2: 4×5 min at 110% FTP, 4 min rest

• Week 3: 4×6 min at 110% FTP, 4 min rest

• Week 4: Deload or retest FTP

Next block, switch levers:

• Week 1: 4×4 min at 112% FTP, 4 min rest

• Week 2: 4×4 min at 114% FTP, 4 min rest

• Week 3: 4×4 min at 116% FTP, 4 min rest

• Week 4: Deload or retest

Key Takeaways

• Two levers for VO2max progression: interval duration and intensity percentage

• Moving both simultaneously kills your ability to diagnose what's working

• One lever per block, progressed steadily across 3–4 weeks

• Duration lever: keep % fixed, add time per interval each week

• Intensity lever: keep duration fixed, raise % of FTP each week

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